This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Research studies indicate that consumption of isoflavone-rich soy lowers prostate cancer risk. The soy components thought to be responsible for this effect are the soy isoflavones (phytoestrogens). As a result, isoflavones are currently being investigated in epidemiological and clinical studies for their possible roles in prostate cancer prevention. It is extremely important in these studies to have an accurate estimate of isoflavone exposure in individuals. Given the inadequacy of dietary methodolgies, biological fluids are considered more reliable indicators of exposure to isoflavones. In designing these studies, researchers have generally assumed that plasma and urinary isoflavone concentrations accurately reflect prostate tissue exposure. However, at this time, no information is available on the validity of this assumption. Thus, the main objective of this proposal is to evaluate the reliability of plasma and urinary isoflavone levels by comparing blood and urine concentrations to more direct measurements of prostate exposure. In order to accomplish this goal, the current study will compare isoflavone levels in plasma and urine with those in expressed prostate secretion (EPS), a widely accepted marker for prostate tissue exposure.